The recent sharp rise in the cost of gasoline has instigated a search for alternative methods to power automobiles. One such alternative method is electricity provided by one or more newly developed high temperature batteries. However, such batteries require an insulated enclosure or their efficiency will be reduced to unacceptable levels.
Insulation panels to be used to construct such an enclosure must satisfy a number of criteria. Because of the high temperatures involved on the inside of the enclosure, which are on the order of 800.degree. F., the insulation panel must have excellent high temperature insulating qualities and not degrade either physically or in terms of heat resistance capability upon exposure to such high temperatures or due to the stress imposed by the temperature difference between such high temperatures on one side of the panel and the ambient temperatures on the other side of the panel.
Another criteria which must be satisfied by insulation panels in order to be suitable for use to construct high temperature battery enclosures is load bearing capability. This is because the insulation of the high temperature battery is greatly abetted by a vacuum space between the high temperature battery and the ambient conditions. Such a vacuum results in a load upon the insulation panel of atmospheric pressure of about 15 pounds per square inch (psi). This is in addition to any other load the insulation panel might have to bear due to the limited space available on a vehicle for battery placement which might necessitate the use of such insulation panel as a platform to support other weighty accouterments of an electric vehicle.
A further criterion necessary for suitable insulation panels is that they be light in weight. Heavy insulation panels would work to defeat the purpose of an electric powered vehicle wherein light weight is of prime importance.
In summary, insulation panels suitable for use to insulate a high temperature battery enclosure must have excellent high temperature insulating qualities, must be able to withstand the stress caused by extreme temperature difference between the sides of the panel, must be able to bear a significant load, and must be light in weight. Unfortunately, in general, material qualities which impart to insulation ability to address any one of the above criteria tend also to reduce the ability of the insulation to adequately perform to meet one or more of the other criteria. For example, material qualities which increase the insulation's load bearing capability also tend to increase its weight and decrease its insulation capacity.
Insulation which can be used to form an enclosure is known. For example, U.S. Pat. No. 3,094,071--Beckman discloses a double-walled tank for cryogenic fluids wherein the space between the walls is evacuated and the walls are supported by spacers made of ceramic or thermal-setting plastic reinforced with fabric or paper. U.S. Pat. No. 3,289,423--Berner et al teaches the use of pegs made by gluing together layers of glass fibers to support vacuum insulated panels. U.S. Pat. No. 3,161,265--Match et al teaches pegs of glass reinforced phenolic resin to prevent wall deformation in a heat insulating vacuum panel. This patent suggests that ceramic pegs be used when high temperatures are involved.
None of the known enclosure forming insulation, such as those described above, are satisfactory for use to construct a high temperature battery enclosure for an electric vehicle. This is not surprising since the need for such an enclosure has only recently arisen. High density support pegs such as those made of ceramics have the disadvantage of relatively high thermal conductivity at elevated temperatures. To reduce heat transfer, the peg support area must remain small, thereby diminishing load bearing capability. Pegs containing binders or resins provide a continuous conductive heat path thus reducing insulating performance. Moreover, such binders or resins may give off vapors at elevated temperatures thereby degrading the vacuum and further reducing insulating performance.
It is therefore an object of this invention to provide an insulation panel having excellent high temperature insulating qaulities.
It is a further object of this invention to provide an insulation panel which can easily withstand the stress imposed by relatively large temperature differences on either side of the panel.
It is still a further object of this invention to provide an insulation panel which is capable of bearing a significant load.
It is yet another object of this invention to provide an insulation panel which is relatively light in weight.